This invention relates to an ink jet nozzle plate of a thermal ink jet printer and, more particularly, an improved polymeric ink jet nozzle plate of a thermal ink jet printer.
A major component of a print head of a thermal ink jet printer is a nozzle plate. The nozzle plate has a surface adhered to a surface of a semiconductor substrate on which are disposed numerous thin film heat resistors.
The nozzle plate has a plurality of bubble or firing chambers equal in number to the number of resistors on the semiconductor substrate. The resistors are disposed in the bubble or firing chambers.
Each of the bubble or firing chambers communicates with a separate ink supply channel. The separate ink supply channels communicate with a supply source of ink.
The nozzle plate also has passages, equal in number to the number of bubble or firing chambers. Each of the passages extends from one of the bubble or firing chambers through an orifice or port in a surface, which is parallel to the surface adhered to the semiconductor substrate. The droplets of ink are selectively expelled through the orifice or port for printing after the ink is selectively heated by the resistor.
One problem with the prior nozzle plates of thermal ink jet printers has been the accumulation of air bubbles in the bubble or firing chambers. The presence of an air bubble in the bubble or firing chamber can cause operational and print quality problems ranging in severity from moderately diminished jet velocity to severely anemic and misdirected jets of ink exiting through the orifices or ports of the nozzle plate.
It has been previously suggested to form a polymeric nozzle plate in which each of the bubble or firing chambers has the same configuration as the resistor on the semiconductor substrate and only slightly larger such as five microns, for example. While this minimizing of the dimensional differences between the walls of the bubble chamber and the periphery of the rectangular shaped resistor has reduced the size of any accumulated air bubble, air has continued to accumulate in the corners of the bubble or firing chamber where the rectangular shaped chamber meets a circular conical passage through which the ink is supplied to the orifice to be expelled as an ink droplet.
It has been discovered that decreasing the surface tension of the ink helps to reduce the adhesion force between any formed bubble and the wall of the bubble or firing chamber. The tension of the ink surface has been reduced by addition to the ink of surface active agents or low surface tension bulk additives. This reduction in the ink surface tension has permitted the air bubble to be more easily swept out of the passage under the action of jetting.
However, because of the surface active agent in the ink, the ink accumulates in puddles on the exterior surface of the nozzle plate having the orifice or port so that an emerging ink jet is pulled off center relative to the orifice or port through which it exits whereby the droplets of ink are deflected away from the intended spot on a recording medium. The additives also may adversely influence print head operation or print quality.
The nozzle plate of the present invention solves the problem of air accumulation in the bubble or firing chambers of a nozzle plate through eliminating geometric features that might trap the air. This is accomplished by changing the shape of each of the passages extending through the nozzle plate from a circular cone to a converging rectangular shape through the entire thickness of the nozzle plate.
Thus, with the resistor disposed in the largest end of the passage extending through the nozzle plate and the passage having a continuously converging rectangular shape until the orifice or port is reached, there is no intersecting surface on which the air bubbles can accumulate.
An object of this invention is to provide an improved nozzle plate for a print head of a thermal ink jet printer.
Other objects of this invention will be readily perceived from the following description, claims, and drawings.